May 20, 2016

it has been lot of research carried out on the capacity of roads, transit or pedestrians infrastructures, with results proven empirically. Such don’t really exist for the cycle tracks, but as the success of the London’s “Super cycling highways” shown, it will become a significant matter

NACTO, in a recent publication [8], estimates the capacity of a 2 way bike lane (3 to 3.50m) at 7,500 bike/hour. This number seems to be derived of the Highway Capcity Manual citing very dusty publications [1]. this post argues that the capacity of a bikeway is more in the 1,500 cyclist/hr/lane (where a lane is 1.20m to 1.5m wide)

A short Litterature review

Most of the papers trying to estimate a bike lane’s throughput tend to rely either on mathematical models, experiments or a blend of both:

An example of experiment leaded by [2] to determinate a bike lane throughput. The experiment above has allowed [2] to conclude that the capacity of a bikelane should be in the 2,500 bike/hr range

The problem of such approaches is they are not (yet) validated by practice (…and in some case, the experiments seem to be more representative of a velodrome typology than an urban bike lane). They also tend to provide a great range of result: One literature study [3] found a capacity of 1,500-5,000 cyclists per hour and traveling speed around 12-20 km/h. Another literature study [4] found a capacity of 2,000-10,000 cyclists per hour for a 2.5 m wide cycle track. It is also important to notice that all these numbers concern an uninterrupted bike lane (e.g bike lane with no intersection).

However, [5] ( as cited by [6] ) reported that the theoretical and practical capacities of a Chinese bicycle lane are about 2000 bicycles/h/ln and 1280 bicycles/h/ln, respectively… That is also in line with an empirical result presented by [7] concerning the Denmark:

How much lanes of cyclists fit in 3.5m width bikeway[7] tend to answer to it:

If a 1.8 to 2 m wide bikeway fit 2 lanes of cyclists, any additional lane could require a 1.20m additional width (notice that the cyclists could have a tendency to ride in quincunx to increase their available lateral room). That is the reason for the suggested significant increase in capacity as soon as an unidrectional bike lane reach 3m in the graph above. (There is also some reasons to believe that a 4 meters bidirectioanl bike lane is not width enough to enable 2 lanes of cyclists in each direction in a sustainable way: see video below)

Validation of the numbers in practice

Up to recently, it was basically no opportunity to validate a bikelane model capacity in real life. China of course has wide and busy bike lanes, but they has never presented a typology directly applicable to Europe or America, be by their different geometry or by the type of vehicle: many trikes (up to recently), and nowadays those bikelane tend to be overwhelmed by sccoter (electric or not) (- 70% in Hangzhou as measured by [6]. Bikes also tend to move much more slowly). However, with the recent opening of the London cycle highway this things could change:

This video represent the cycling traffic on the London’s Blackfriars bridge: The incoming lanes presents the symptom of a bikeway reaching capacity (bike moving slowly, at speed apparently just enough to maintain balance, and the rare occasional take over use the opposite lane)

What is the effective throughput of Black friars Bridge bike lane?

Sure enough, some cycling supporters quickly raised the question while some other provided some numbers. Here are ours

there are 37 incoming cyclists crossing a a line (represented by the bottom of the video)

there are 24 outgoing cyclists crossing the same line

that represents an “instant” throughput of 11,000 cyclists/hour on a period of 20s, or ~3,300 cyclists/hour/ln in the busiest direction (or the equivalent of 10,000 cyclists/hour per car width lane).

First issue, Instant throughput ≠ Throughput

Traffic tends to not flow homegeneously (move in wave, aka “stop and go” traffic), and a measure on 20s can’t be directly scaled into a more generalized throughput. [7] faced with similar issues applied a correction factor based on freeway traffic observation (by comparing maximum observed traffic volumes in 15 minute intervals and maximum volumes in 10 and 20 sec intervals on freeways): this correction factor is estimated to be 0.63

The estimated maximum throughput per lane observed on the Blackfriar Bridge video above become closer to 2000bile/hr/lane. Still a sustantial number (but already significantly less than the number touted by NACTO), a number also in agreement with theorical number exposed by

There are right and left turning cyclists, which fatally indhers the capacity of a bike lane…and there are signal controlled intersections (a necessity as illustrated by the difficulty of the cyclist, waiting at an intersection, to integrate itself in the main bike lane). As for motor traffic, all these tend to halve the real capacity of a typical interrupted urban bike lane vs an hypothetcal uninterrupted one. So that the real capacity we could measure here tend to be more in the ~1,000 to ~1,700 bike/hr/ln (according to if we apply a correcting factor or not). Those numbers are also in line with results from the field carried by [5] and [7]

Why all that matters?Notice the 2 double deckers in one lane, seen in less than 30s: Could we conclude that the transit capacity of this lane is 24,000people/hour?

It matters since wrong numbers could lead to wrong decisions on the allocation of the street space, but also on the “right sizing” of a bike infrastructure.
The matter is of importance, essentially in regard of transit:

There is no question that a bike lane can achieve a very high throughput but does a 3.5 meter bike lane can carry as much as people than a tram or a BRT?

According to NACTO, a bus lane (BRT) can carry 4,000 people (8,000 if train): Those number thought slightly optimistic [9] are fairly realistic, and can be verified empirically…Here we infer that a bike lane of similar width (3 to 3.5m) can be competitive with a buslane but not a trams transit system, in term of throughput.

Furthermore we have not touched the whole notion of Level of Service: the mentioned capacity for Transit are design capacity, that is capacity allowing the transit system at its design (optimal) speed. Reaching the capacity of the bike lane as measured on the BlackFriars Bridge tend to infers a degradation of the speed for cyclists (at least by queuing at traffic light). We also didn’t touch the bike parking issue

[1] the third edition of the Highway capacity Manual suggests a capacity range of 1700-2500 bicycle/hr/ln where each lane is 3 to 4 feet. Those numbers are inferred of previous publication (“bikeway planning design and guideline” institute of traffic and transportation engineering University of California at Los Angeles 1972, “Geometric Design” by W. King, C., and Harkens, in Transportation and Traffic Engineering Handbook, Institute of Transportation Engineers, 1972). the 7,500 number touted by the NACTO correspond to the highest range of it considering that a 3.5m wide can feet 3 lanes of bike

May 21, 2013

…or perceived safety and objective safety of the cycle tracks

A study on Toronto and Vancouver (Canada) from [4]: the risk of bike infrastructure separated of traffic is under-estimated. Note the result carried for the cycle track is an aberrant and irrelevant one for reason explained in [8]

Usually, Urban segregated bike lanes (cycle tracsk) are perceived as safer than non segregated one, by many cycle advocates and public alike. Alas most accident statistics say otherwise, and most scientific studies conclude, consistently overtime, that segregated bike lanes impair safety by ~20% ([1] summarizes and complete previous studies, see also a list of studies at [9]), some older studies putting this number up to 4 time higher [2].

Of course, it is possible to find some studies saying otherwise, but usually those studies show significant methodology shortcomings. To focus only on recent Canada centric examples: [5] draws conclusion on cycle track from a field study conducted in cities not having such infrastructure per sei, as seen in [8] and obvious selction biais discredit results from [3] (more critics here and there):

Montreal, QC: In (3), a separate bike path in a one lane residential street (rue Brebeuf) is compared to an up to 6 lanes thoroughfare (rue st Denis) on a 1km section (Rachel to Laurier), where St Denis has more intersection, and higher speed limit than Brebeuf...to conclude that separates bike lane improve cyclist safety! (no indication of motor traffic volume is provided) -

The most recent study extended to the USA by the same authors, [10], seems to suffer similar flaws [11].

In urban area, most of the cyclist accidents are due to conflict with motor vehicles (85% in French cities according to the OSNIR), and most of them occur at intersection: In Canadian cities, 50% of fatal accidents and 72% of accidents resulting in serious injury occurred at intersections [12].

Thought, that a separated bike lane can remove potential conflicts along a road, and is recognized to reduce risk in such cases, it makes matter worse at intersections: This is mainly due to the fact cyclists, not on the road, tend to be overlooked by other road users, generating conflict at road intersections. The increased risk for cyclist is illustrated below:

According to (2), the cyclist could be up to 12 time safer on the right side of the street - credit photo (6)

Aware of this fact, Some transportation professional organizations don’t recommend separated bike lane: it is the case for the AASHTO in the USA, or the CERTU for urban area in France. A position supported by numeorus cyclist organizations, be in France (FFCT, Fubicy) or Germany (ADFC), which have been at best rather neutral on the development of segregated cycle track, in some case opposed, and consistently advocating against the mandatory use of it. That eventually became the case for most of the french cycle track, circa 2000. For this later purpose a new road sign has been introduced, and Germany is following track:

The cycle in a blue square sign has been introduced circa 2000: it indicates a recommended cycle track. The cycle in a blue disc indicate a mandatory cycle track ... except of course in UK Which has not ratified the Vienna convention on road sign, from which those signs are derived

An issue is that motorists tend to ignore the difference, and harass cyclists not using the cycle tracks

Traffic engineers, on their side, sometimes eager to remove cyclist of the road for their “good”, have worked to increase the safety of separate bike lane:

Reintroduction into general traffic at intersection

Rennes, France (Armorique Bld): Cycle track merging in general traffic at intersection, and resuming after it

Treating cyclist as pedestrian at intersection

Hong Kong (Along Ting Kok Rd, Kong Kong NT): Cyclists are expected to walk their bikes to the cycle track... and dismount at every intersections...what by the way is seldom respected in despite of the British style staggered pedestrian crossing! -credit photo left (16), right, Google

Cycling Commuters are generally not impressed by those treatments, which are just slowing down their commute, even when the obligation to walk the bike at intersections (Hong Kong case), is obviously widely disregarded by cyclists using such facilities.

It has been “invented” in Copenhagen in 1981: The basic idea is to mark the area of conflict between motor vehicles and cyclists so road users pay more attention to this conflict and cyclists have a lane marking through the junction area. Alas, while it is found effectively reducing the number of accidents (and injuries) with one line, it increases it with 2 lines or more, according to [13].

A reason for that is that, it becomes too much solicitation for the motorist than he can process – resulting in an increase of rear ending collisions and red light runnings; and provides a false “sense of safety” to the cyclists, becoming more complacent- not doing head check or using hand signals according to [14]– what is consistent with the “naked street and risk compensation theories.

Supporters of the helmet laws are because they are concerned by the safety of existing cyclists, they will be obviously against separated bike lanes for the same reason. Not surprisingly, most of the anti cyclist lobbyist will fell in this category

Supporter of the helmet laws supporting separated bike lane are not logical with themselves and probably grossly misinformed

Opponent to the helmet laws, will explain that, while the safety of existing cyclists is important, it is not paramount- One have to take a more holistic view to assess the benefit/drawback of such safety tool than the existing cycling population- and opponent to the helmet laws, without necessarily denying the positive safety effect of the helmet on an individual, will oppose to a law on the ground that it discourages sufficiently cycling to have a general negative effect for the society.
Same logic apply to the cycle tracks: there is no need to deny their negative effect on road safety, or to produce biased studies to try to counter evidence, to support them: that is only conductive of complacency with poorly designed cycle tracks which do no good for cycling. Former Vancouver Planning Director, Brent Toderian was able to implicitly recognize the safety issue and supporting it [17]: What is important is to produce evidence that the positive effect they induce outweigh their negative ones

[8] Conclusion of both [4] and [5] are drawn from a study carried from May 2008 to Nov 2009 in Toronto and Vancouver. To the bets of our knowledge, it was no “cycle track” in Toronto, and the only ones able to qualify in Vancouver, were an experiment started on July 2009 on Burrard Bridge, with no intersection along the ~1km cycle track segment, and a ~300m segment in one direction on a quiet street (Carral street) with ~300 cars at peak hour with only one very quiet intersection (Keefer street) featuring ~120 car at peak hour (From City of Vancouver’s 2006 traffic count) what is barely representative of a typical cycle track: The result provided for the cycle tracks is hence certainly irrelevant, and that is the reason it stands as an outlier.

[11] [10] draws conclusion by comparing current crash rate on some cycle tracks with some numbers collected, sometimes in specific situation- like a study on Boston’s bike messengers- more than 10 years ago, without correcting them of external factors, like significant general crashes reduction rate in the last decade, and well documented safety in number effect affecting more particularly the cyclists. Furthermore, one could argue that the “crash rate” is a very poor, if not uncorrelated, proxy, to qualify the safety of a road infrastructure: Roundabout are well-known to increase the rate of crashes, vs a signaled intersection, but they are also well recognized to reduce the risk of serious injuries, most of the crashes being limited to fender-bender type. In other word, a crash rate ratio is not representative of the safety social cost of an infrastructure…what ultimately matter. More awkward [10] suggests that “The AASHTO recommendations may have been influenced by the predominantly male composition (more than 90%) of the report’s authors” without being able to substantiate this assertion, showing that we have here more a opinion paper: attacking the gender of authors to disqualify their works, seems pretty petty at best!

[15] The finding of [13] seems in fact to suggest that the increase in accident and injuries are mainly among motorists, and eventually moped: so that in fact the blue line could effectively be not than “unsafe” for cyclists. Unfortunately, the paper doesn’t provide detailed break down of the injuries according to the transport mode. In any case, the measured global effect is a negative one